Sun Protection Basics

8/7/2019 Sun Protection Basics

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Sun protection basics

Considering that sun damage is the primary environmental factor in skin aging and skin cancer, wehighly recommend that you thoroughly research the topic of UV protection, starting with reading allarticles in this section.

In this article, we provide the summary of basic guidelines and principles to help you jumpstart yoursun protection strategy. You can start here, but don't stop here - learn more to optimize your sunprotection.

The very basics

Here are the key UV-protection measures adapted from the recommendations of the American

Academy of Dermatology:

y Plan outdoor activities early or late in the day to avoid peak sunlight hours between 10 amand 4 pm.

y Avoid tanning beds.

y Wear a broad-brimmed hat and sunglasses.

y Sit in the shade whenever possible.

y Wear protective, tightly-woven clothing.

y Use a broad-spectrum sunscreen with a SPF of at least 15 on all exposed skin, including thelips, even on cloudy days.

y Use a water-resistant sunscreen if exposed to water, either through swimming or sweating.

y Apply sunscreen 20-30 min prior to exposure and reapply frequently. (See our article oncorrect sunscreen application.)

Note: Please keep in mind that children tend to spend more time in the sun and need extra protection.SeeAAD recommendations on protecting kids from the sun.

Basics plus

In addition to the basic AAD recommendations, many experts consider a number of steps worthwhile,especially for people who wish to minimize skin aging:

y Chose a comprehensive UVA+UVB blocking sunscreen with well-matched UV blockingagents and low risk of adverse reactions. If you have sun-sensitive skin, use SPF 30 or higherfor UVB and similarly strong UVA protection (see our article on choosing the right sunscreen.)

y Use extra caution near water, snow and sand as they reflect the damaging rays of the sun,which can increase your chance of sunburn and skin damage.

y Do not neglect UV protection when indoors or driving. (See our article on indoor UVprotection).

y Ensure vitamin D status safely through a healthy diet that includes vitamin supplements. Don'tseek the sun. (See our article on how to minimize the downside of low sun sxposure)

y Make sure your sunglasses protect from both UVA and UVB and, ideally, cover as much ofyour face as possible.

y Consume diet (and possibly supplements) rich in nutrients that may reduce the severity of UVdamage (e.g. lycopene, green tea, etc.).

Ultraviolet radiation indoors: What you

don't know can hurt you.


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y If you never venture outside, never walk in open air, spend your entire existence betweenyour office, home, car and supermarket - well, that is not fun. You might think that the upsideof such a lifestyle is to never have to worry about sun damage. I'd have to disappoint youagain. Indeed, you won't have to worry about sunburn and could worry less about skin cancer.However, being indoors does not protect you from the kind of UV damage that causes skinaging. There are two kinds of ultraviolet radiation that affect the skin: UVB and UVA. UVB (theone that causes sunburn) does not generally get indoors whereas UVA (the one that causes

skin wrinkles) does so with relative ease. (See our article on ultraviolet radiation to betterunderstand the relationship between UV rays and skin damage.).

y Glass and UV protectiony Most people believe that ordinary window glass blocks UV radiation, making any other UV

protection unnecessary indoors. This is half-truth at best. Window glass blocks UVB but letsmuch of UVA through. The percentage of UVA that passes depends on the type of glass andthe type of coating on the glass. Window glass falls into three major categories: ordinary(clear) glass, reflective glass (allows to see in one direction much better than in the oppositeone), and tinted glass. While all these types of glass block UVB, their capacity to block UVAvaries considerably. As architectural fashion keeps moving towards larger windows, theimpact of these differences is continuing to grow.

y Clear glass allows up to 75% of UVA to pass. Tinted and reflective glass absorbs more of theUVA but still allows about 25-50% to pass; they also have the shortcoming of blocking moreof the visible light than clear glass. There is also the so-called Low-E (low-emissivity) glass,

developed to minimize heating and cooling costs. As far as UV is concerned, regular Low-E(the ones w/o special anti-UV coating, etc.) behaves similarly to clear glass: most UVB isblocked, most UVA gets through.

y The best protection comes from the types of glass specially geared towards blocking UV rays,such as laminated glass and UV-blocking coated glass. Both filter out from 95 to 99% of allUV light. Neither is common in residential or commercial structures. Laminated glass, made oftwo layers of glass with a plastic layer in between, is used in some public buildings, such asairports and museums; it is also used for automobile windshields. UV-blocking coated glass isalso used largely in special circumstances. All in all, whenever indoors, don't assumeprotection from the windows against UVA unless you know that special glass in installed.

y UV protection indoors y If your home and office have special windows with full spectrum UV protection (see above),

you can consider yourself a lucky exception. Otherwise, if you want to minimize skin aging,you need to protect yourself from indoor UVA exposure.

y If possible, use window blinds or shades during peak sun hours. Arrange workspace andsitting/recreation areas not to be too close to the windows. As a minimum, they should not bein direct sunlight. Indoor UVA intensity decreases as the distance from the window increases.If you have large windows, you may want to avoid spending too much time close to thewindows, even if sun is not shining into the room directly. The above steps should reduceindoor UVA exposure to acceptably low levels. However, if you feel that the indoor areaswhere you spend a lot of time receive too much daylight, you may consider additionalprotective measures. This may include additional window blinds or shades, sufficient clothingand sunscreen. If you spend some of the time outdoors, you need a good, strong sunscreenanyway. Otherwise, a moderately robust sunscreen with good UVA protection applied to faceand neck should suffice. Many popular moisturizers provide moderate sun protection asanextra feature. Such a moisturizer may be a good choice for indoor UV protection as long as itadequately covers UVA range.

y UV protection in carsy In the modern world, people are spending ever greater portion of their time in cars. This trend

is likely to continue unless rising fuel costs and/or global warming bring about major changesin our transportation habits.

y In the majority of modern cars, the windshield is built of laminated glass that blocks all of UVBand the vast majority of UVA. However, the side and rear windows are usually made fromnon-laminated glass and let much of UVA through. Clear non-laminated car windows allow upto 60-70% of UVA to penetrate. Tinting reduces UVA penetration to about 15-30%, a muchbetter but still significant level.


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y If your car has clear glass windows, you can add tinting at a qualified auto shop. However,make sure the facility can guarantee compliance with the federally mandated standard of 70percent of minimum visible light transmittance through the windshield.

y There are other factors influencing UVA exposure in the car: you position (the closer you areto a non-laminated window, the greater the exposure), direction of driving relative to the sun,

time of day/year, etc. However, people rarely have much control over any of these. Therefore,you should still use sun protection measures while in the car, such as sunscreens, protective

clothing, and so forth.y Fluorescent lightingy There are two common urban myths about fluorescent lighting and UV exposure. The first

myth says that fluorescent lighting generates hazardous amounts of UV rays, rivaling directoutdoor sun exposure. The second one says that the first myth is complete nonsense and thatfluorescent lighting generates no UV rays whatsoever.

y The reality is a bit more complicated. Most fluorescent lamps work on the following principle.Inside the lamp, electrical discharge excites a gas (usually neon or mercury vapor in argon),which emits ultraviolet radiation. UV rays hit a special dye covering the bulb, which absorbsUV radiation and emits visible light. In this process, most of the UV radiation is absorbed (or

otherwise blocked) by the fluorescent dye and/or the glass of the bulb. Yet, some does getthrough.

y Fortunately, it seems that typical exposure to the UV light from commonly used types offluorescent lamps is relatively small. According to the report by the UK Health Protection

Agency, fluorescent lighting may add about 3% to the lifetime UV exposure. However, thisestimate is imprecise and some lamps may be greater offenders than others. If you spend alot of time under intense fluorescent light, you could consider extra protection. One possiblestep is to ensure that fluorescent bulbs have plastic diffusers over them. Depending on thematerial used in the diffuser, UVA would be reduced by 17-99% and effective UVB by 19-100%.

Ultraviolet radiation: the sun's death ray

The reason sunlight and tanning beds are bad for your skin is ultraviolet radiation (UV-light or UV-raysfor short), which represents a small but important portion of the sunlight spectrum. UV is a killer ofliving things: it can damage almost any part of the cell, but especially its blueprint, the DNA. Suntan,

which is the accumulation of UV-blocking pigment melanin, is a defense mechanism whereby the skintries to protect itself from destruction.

There are three subtypes of UV light: UVA, UVB and UVC.

y UVA (320-400 nm wavelength) is at the long end of the UV spectrum. UVA ratiationpenetrates deeper into the skin and is the major contributor to skin aging and wrinkles. It alsocontributes to the development of skin cancer (along with UVB). UVA rays pass throughordinary glass. UVA is sometimes divided into two subtypes: long UVA (a.k.a. UVA-1, 350-400 nm wavelength), and short UVA (a.k.a. UVA-2, 320-350 nm wavelength). Thissubdivision is important because some UVA sun blocking agents cover only UVA-1 or UVA-2rather than the entire UVA range.

y UVB (280-320 nm wavelength) is the middle range of the UV spectrum. UVB causes sunburnbut has a relatively modest effect on skin wrinkles because most of it is absorbed in the

epidermis (the outer skin layer) and does not reach the dermis where wrinkles form. It alsocontributes to the development of skin cancer (along with UVA).

y UVC (100-280 nm wavelength) is at the short end of the UV spectrum. UVC is the harshesttype of UV radiation. Luckily, UVC is almost completely absorbed by the ozone layer anddoes not reach the Earth's surface. As long as we haven't destroyed the ozone layer, we don'thave to worry about the UVC.

UV index


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If you are not prepared to take measures for maximum possible UV-protection every single day, youcan use the UV index to get an idea when to take UV-protection more seriously. Even though even acloudy winter day at a high latitude can produce sun damage, not all days/locations are created equal-- some are much harsher on your skin then others. Enter the UV index. The UV index is an standardinternational measure of how strong the ultraviolet (UV) radiation from the sun is at a particular placeon a particular day. You can find out about UV index at a given time/location in your area atweather.com or similar websites.

The UV index uses a roughly linear scale, approximately between 1 and 10. "Roughly linear" meansthat two hours of exposure at UV index 1 are approximately equivalent to one hour of exposure at UVindex 2.

The US Environmental Protection Agency provides some basic recommendations for UV protectionbased on the UV index. Below is a brief summary of EPA recommendations (for more details, seeEPA website).

y UV Index 0-2: Low danger to the average person. Wear sunglasses; use sunscreen if there issnow on the ground, which reflects UV radiation, or if you have particularly fair skin.

y UV Index 3-5: Moderate risk of harm from unprotected sun exposure. Wear sunglasses anduse sunscreen, cover the body with clothing and a hat, and seek shade around midday whenthe sun is most intense.

y UV Index 6-7: High risk of harm from unprotected sun exposure. Wear sunglasses and usesunscreen having SPF 15 or higher, cover the body with sun protective clothing and a wide-brim hat, and reduce time in the sun from two hours before to three hours after solar noon(roughly 11:00 AM to 4:00 PM during summer in zones that observe daylight saving time).

y UV Index 8-10: Very high risk of harm from unprotected sun exposure. Same precautions asabove, but take extra care - unprotected skin can burn quickly.

y UV Index 11 or higher: Extreme risk of harm from unprotected sun exposure. Take allprecautions, including the following: wear sunglasses and use sunscreen, cover the body witha long-sleeve shirt and pants, wear a broad hat, and avoid the sun from two hours before tothree hours after solar noon.

Keep in mind that UV index data, their interpretations and EPA recommendations have importantlimitations. In particular, the UV index is weighted more towards UVB frequencies and tends to

underestimate UVA exposure.In other words, the UV index is more useful in assessing the risk ofsunburn than long-term damage to the dermis and skin matrix that leads to wrinkles. In fact, low

values of the UV index may, in certain situations, underestimate the impact of sun exposure on skinaging. Therefore, if you are concerned with skin aging you may want to be even more proactive than

the EPA guidelines recommend.

UV exposure vs. season, time ofday and latitude

Most people know that UV exposure is highest around noon and in early afternoon, in the summerand at low latitudes. Correspondingly, EPA recommends to reduce time in the sun between roughly11:00 AM to 4:00 PM during summer in zones that observe daylight saving time. However, things arenot as simple as they might seem. Indeed, UV intensity varies dramatically during the day as well asbetween seasons and across latitudes. (See the charts of radiation intensity vs time of day/year forUVA and UVB. For example, a sunny winter morning in Canada presents virtually no risk of sunburn,

whereas a sunny summer noon in Egypt virtually guarantees it (assuming no sun protection). Yet,sunlight can contribute to skin aging even outside peak hours, summer season, or low latitudes. Thisis partly due to the fact that skin aging is caused predominantly by UVA. While both UVA and UVBrise towards midday, summer and lower latitudes, the changes are much less dramatic for UVA thanfor UVB. As a result, non-peak levels of UVA may be considerable compared to its peak levels (muchmore so than for UVB). Therefore, if you wish to minimize skin aging, you should expand your UV-protective measures beyond just midday, the summer and low latitudes.

Indirect sunlight


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Much of UV radiation remains in the sunlight when it is reflected from the majority of commonsurfaces or refracted via clouds or water. When outside, don't assume that wearing a hat or staying inthe shade fully protects you. Reflected sunlight may retain over a third of its UV rays. In particular,your UV exposure is much higher on the snow and water. Even beach sand reflects 20-30% of UV.Beach goers and skiers should be especially thorough regarding UV protection measures.

Clouds, except perhaps on a heavily gloomy day, cannot be relied upon for UV protection. A thin layer

of clouds reduces UV intensity by only 20-40%. Water is a similarly weak protector: twelve inches ofpool water would also reduce UV intensity by only 20-40%.

Clothing can be more or less protective, depending on thickness, color, fabric type and many other

factors. Wet clothing is less protective than dry clothing - up to 50% of UV penetrates wet clothing.

Indoor UV light

You may have heard that glass blocks UV rays. It does block UVB quite well but often fails to blockmuch of UVA. The degree of indoor UV exposure depends on light intensity, type of glass and otherfactors.

Sunscreen fundamentals: howsunscreens/sunblocks work

Using sunscreen should be an important part of a comprehensive sun protection. To take fulladvantage of sunscreens, you have to be able to select a sunscreen that is both effective and a goodfit for your particular situation (skin type, lifestyle, esthetic needs and so forth). To that end, it is usefulto understand how sunscreens work, what impacts their effectiveness, what potential risks are, and soforth. These issues are discussed below.

UV blocking mechanism. Chemical and physical sunblocks.

UV radiation may be blocked either by absorption or reflection/scattering of UV light. Based on their

mechanism of protective action, sun-blocking agents are broadly divided into physical and chemical.

Physical blockers are usually finely powdered and dispersed minerals, the most common being zincoxide and titanium dioxide. They block UV radiation mainly by reflecting/scattering the rays. They areinsoluble under typical conditions and only minimally absorbed into the skin. As a result, they are easyto rub off and may need to be reapplied especially frequently. Also, when applied to the skin, bothzinc oxide and titanium dioxide create white-tinted matte look. To reduce this unsightly effect, somemanufacturers employ microfine zinc oxide and/or titanium dioxide with particles smaller than 200 nm(a.k.a. nanoparticles). Such formulations are more transparent but raise concerns about possiblepenetration of nanoparticles into the skin and accumulation in vital body tissues.

Chemical sunblocks work mainly by absorbing UV light. Most are synthetic chemicals that are solublein oil and/or water. Many are absorbed into the skin and, possibly, into systemic circulation (and,therefore, need a thorough safety testing). Some degrade when exposed to UV radiation and/or

interact with other sun-blocking agents or other cosmetic ingredients.

There are a few agents that act as both physical and chemical sunblocks. One such hybrid sunblockis bisoctrizole (Tinosorb M). Even though titanium dioxide is typically considered a physical sunblock,some experts consider it a hybrid because considerable part of its activity is through UV absorption.

Overall, physical sunblocks tend to have broader spectrum of UV protection and appear somewhatsafer due to the lack of systemic absorption. On the other hand, they are more unsightly (especiallythe safer, not-microfine versions) and require more frequent application.


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In any case, each sunblock, physical or chemical, has its own unique profile and should be evaluatedindividually. (See our information on individual sun-blocking agents.)

Range ofUV protection

There are three subtypes of UV light: UVA (320-400 nm wavelength), UVB (280-320 nm), UVC (100-280 nm). UVA is sometimes subdivided into UVA-1 (350-400 nm) and UVA-2 (320-350 nm). UVC is

almost completely absorbed by the ozone layer and does not reach the Earth's surface. As long as wehaven't destroyed the ozone layer, we don't have to worry about the UVC. But we do have to worryabout the other two. UVB causes sunburn, but has a relatively modest effect on skin wrinkles becausemost of it is absorbed in the epidermis (the outer skin layer) and does not reach the dermis wherewrinkles form. UVA penetrates deeper into the skin and is the major contributor to skin damage andwrinkles. Both UVA and UVB can contribute to the development of skin cancer. (See our article on

ultraviolet radiation for more details.)

Sunscreens vary in regard to which part(s) of UV spectrum they block. For example, zinc oxide blocksradiation across entire UVB and UVA, titanium dioxide blocks UVB and short UVA (UVA-1), ecamsule

(Mexoryl) blocks UVA only and homosalate blocks UVB only. Whatever sun-blocking ingredients youare using, both UVB and UVA need to be fully covered.

Degree and uniformity ofUV protection

Even if a sun blocking agent works across a particular range, it typically has a peak wavelength whereit is more effective than elsewhere. Also, even in its active range, an agent generally blocks only acertain percentage of UV radiation. The rule of thumb indicator of the degree of protection againstUVB is SPF. There is no widely established protection gauge for UVA; the most commonly used oneis PPD. (See our article on gauging UV protection via SPF and PPD.) Increasing the concentration ofthe a sun-blocking agent, typically increases the degree of protection but may also increase the risk ofskin irritation, toxicity, unsightliness, formulation/application difficulty and so forth.

Stability and interactions

Most of today's sun-blocking agents are stable in inert vehicles at room temperature when notexposed to UV light. However, exposed to sunlight, some may degrade, react with other ingredients in

a sunscreen formula and/or become catalysts of chemical reactions between other ingredients. Thesechanges can lead to loss of UV protection as well as the formation of possibly harmful byproducts. Forexample, when exposed to sunlight, avobenzone and octyl methoxycinnamate (octinoxate) degradeand lose sun-blocking effectiveness whereas some forms of titanium dioxide may exhibit

photocatalytic activity resulting in the formation of potentially harmful free radicals.

The stability of sun-blocking ingredients can sometimes be improved by using photostabilizers,antioxidants, coatings and so forth. For example, a sunblock octocrylene can partly protect fromdegradation other sun blocking agents (e.g. avobenzone). Potentially harmful photocatalytic activity oftitanium dioxide can be reduced by special coating.

Check the sun blocking ingredients in your sunscreen for stability (especially in sunlight) as well aspotentially harmful interactions. (See our information on individual sun-blocking agents.)

Solubility

Solubility is a factor that affects the compatibility of sun blocking agents with certain vehicles as wellas their interaction with the skin. For example, oil soluble sunblocks tend to penetrate skin easier,which, on one hand, may increase the risk of side effects, and, on the other hand, tends to extend thetime of skin protection after an application. Water soluble sunblocks may be particularly useful for low-oil, non-comedogenic sunscreens preferred by many acne sufferers. Sun blocks soluble in neitheroilnor water tend to work mainly as physical sunscreens (i.e. as particles that reflect/scatter UV light);they are only minimally absorbed by the skin. (For specific solubility data, see our information on

individual sun-blocking agents.)


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other limitation as well. It does not take into account stability of the sunscreen, how long it stays onthe skin, water-resistance and so-forth. Still, SPF is a useful ballpark measure of a sunscreen's UVBprotection. The biggest deficiency of SPF is that it fails to take into account UVA, the major contributorto skin aging and some types of skin cancer.

A sunscreen with SPF 15 or higher should provide a good UVB protection as long as it stays on theskin long enough and does not degrade. If you have sun sensitive skin or are exposed to a high peak

of UV radiation (e.g. daytime in tropics), use SPF 30 or higher.

Measuring UVA protection

Protection against UVA is critical if you are to minimize skin aging and reduce the risk of skin cancer.Yet, it is much harder to judge how well a given sunscreen protects against UVA than UVB becauseSPF gauges only UVB.

Many sunscreens don't even mention UVA. Others say that they provide UVA protection but do notspecify its strength. You cannot detect UVA damage yourself without special equipment (such asWood's lamp). And there is no universally recognized SPF-like number to grade UVA protection.

One emerging UVA protection standards is Persistent Pigment Darkening (PPD), which is a biological

measure of UVA radiation absorbed by the skin. A sunscreen with PPD 15 or higher should providegood UVA protection (again, as long as it stays on the skin long enough). Unfortunately, relatively fewsunscreen manufacturers provide PPD values. Some others provide the percentage of UVA asunscreen blocks. (Anything above 90%, which is close to PPD=10, should be satisfactory.)Unfortunately, many sunscreens provide no quantitative UVA-blocking information at all. For those,you can contact the manufacturer and try to obtain the UVA protection information. Unless you get asatisfactory response, you would want to avoid such a product.

Sun protection ratings alone are not enough

If is important that your sunscreen has high ratings for UVB and UVA protection. However, high SPF,PPD and other ratings alone are not enough. It is at least as important that you apply your sunscreenfrequently and generously. Also, keep in mind that some sun-blocking ingredients and/or theircombinations gradually degrade and lose their protective capacity when exposed to sunlight. (See our

information on individual sun-blocking agents.) Sunscreens prone to degradation should be appliedmore frequently, especially during peak sun activity.

How to apply sunscreen

How you apply your sunscreen has a major impact on the quality of the sun protection you get. Butbefore discussing the proper application, let us put the usage of sunscreens in some perspective.

First, sunscreens are less reliable in practice than other UV-protection measures, such as avoidanceof exposure at peak sun hours, protective clothing and so forth. Therefore, sunscreens should be anelement of a comprehensive approach, not a sun damage panacea. (Second, it is important to choose

a good, broadly protective sunscreen that fits your skin and lifestyle

That said, how you apply your sunscreen has a major impact on its effectiveness. The key points ofsunscreen application are discussed below.

Apply liberally 15 - 30 min before expected sun exposure. Sunscreen should be applied insufficient amounts. Most people need at least 1 ounce (about 30 ml) of sunscreen to covertheir body. Do not forget to generously cover the face and neck, even if you wear a hat. If youwish a differently textured formula for the face, find a good sunscreen specially formulated forfacial skin. If your sunscreen includes any chemical sun blocking agents (and most do), give it15 - 30 min to get absorbed into the skin before going out in the sun. Purely physical


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sunscreen (e.g. zinc oxide) can be applied just before exposure. Also, use lip balm or lipstickwith sunscreen on your lips.

y Make sure that easy toforget areas are covered too. Don't forget to cover often-neglectedparts like fingers, toes, nose, and ears (including top of and behind ear lobe). Use lip balm orlipstick with sunscreen on your lips. Use UVA+UVB protective sunglasses but cover the areasaround the eye with sunscreen nonetheless. If you have thinning hair, try sun-blocking

products designed for scalp protection.y Reapply regularly, more often after water exposure. Most experts recommend reapplying

sunscreen at least every two hours, more often if swimming or sweating.

Water resistant sunscreens are available for active individuals or those involved in watersports. It's important to check the label to ensure they say "water-resistant" or "very water-resistant." According to FDA guidelines, Water-Resistantsunscreen maintains the SPF levelafter 40 minutes of water immersion. Very Water-Resistantsunscreen maintains the SPF

level after 80 minutes of water immersion.

There is an ongoing controversy as to what reapplication frequency is optimal. Expertsusually recommend reapplication every two hours. However, some studies indicate thatreapplication every 15-30 minutes after the sun exposure begins is required for optimalprotection. Further reapplication is recommended immediately after sweating, swimming,

rubbing, etc.

Some expert argue that not reapplying sunscreen frequently enough may sometimes lead toalmost as much damage as using no sunscreen whatsoever because degradation products ofcertain sun blocking ingredients promote the formation of harmful free radicals. This is morelikely to be an issue for the sunscreens whose ingredients are known to be unstable under UVlight. In any case, do not rely on sunscreen alone for sun protection and when using

sunscreen reapply frequently and diligently.

y Read the label carefully and follow instructions. Sunscreens may vary in many ways,

including optimal ways to apply them. Make sure you read the label carefully and followmanufacturer's instructions.

The dark side of chemical sunscreens.

Should you be concerned about

photosensitization?

y In the world of medicine, the situation when the remedy may be almost as harmful as theproblem is not uncommon. Skin protection with chemical sun blocking agents might be a casein point, according to some experts.

y First, a little background. Protecting the skin from harmful ultraviolet (UV) rays is important forboth preventing skin cancer and reducing the rate of skin aging. The exposure of the skin toUV rays can be reduced by UV blocking agents (a.k.a. sunscreens, sunblocks, UV/sun

blockers), which fall into two broad categories: physical and chemical.

y Physical blockers are usually finely powdered and dispersed minerals, the most commonbeing zinc oxide and titanium dioxide. They block UV radiation mainly by reflecting/scatteringthe rays. They are generally insoluble and do not penetrate the skin. Conversely, chemicalsunblocks work mainly by absorbing UV light. Most are synthetic chemicals that are soluble inoil and/or water. Many can penetrate the skin at least to some degree. (See our article onsunscreen fundamentals for details.)

y The useful ability of chemical sunblocks to absorb UV light is also a potential source ofharmful effects. When a molecule of a chemical sunblock absorbs a UV photon (a quantum ofUV light), it becomes excited (energized). However, the sunblock molecule does not stay


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excited forever. Eventually, it releases the absorbed energy by emitting lower energy photonsand/or interacting with other molecules. These secondary effects oftentimes lead to theformation of harmful chemical byproducts, particularly free radicals. If this occurs inside theskin (i.e. the sunblock molecule has penetrated the skin before absorbing UV photon), thefree radicals (and possibly other secondary effects) may cause skin damage and irritation,increase the risk of cancer as well as contribute to skin aging.

y The process where a chemical makes the skin (or other tissues) prone to damage when

exposed to light is called photosensitization. There is evidence that at least some chemicalblockers can trigger the production of free radicals and thus cause photosensitization. Inparticular, the following blockers were shown to be potential photosensitizers: octocrylene,octyl methoxycinnamate (octinoxate), benzophenone-3 (oxybenzone) and benzophenone-4(sulisobenzone). More research is needed to determine whether any of these or otherabsorbable chemical blockers can cause significant skin damage under the conditions oftypical use.

y What does this all mean in terms of best practices for sun protection? Should one abandonthe use of all sunscreens containing chemical blockers until they are comprehensivelyresearched and improved? At present, the answer is not clear-cut so let me provide somecontext.

y First, no sunscreen is perfect. Even if there was one, the chances of it being appliedconsistently and correctly are low. Hence the best strategy to avoid UV damage to the skin isto reduce exposure while taking steps to minimize the downside of sun avoidance. When

reducing sun exposure is not an option, physical sunblocks (e.g. zinc oxide and titaniumdioxide) tend to be safer (as long as they are not in the form of nanoparticles). Unfortunately,physical blockers have drawbacks too. They rub off too easily, they may be cosmeticallyproblematic (powdery white) and, more importantly, it is difficult to achieve very high degreeof broad (UVA+UVB) protection with physical blockers alone. Therefore you may still want toconsider chemical sunscreens as an option if facing particularly intense and/or prolonged sunexposure or if your skin is particularly sensitive to the sun and avoidance is not feasible. Insuch a situation, what would be the lesser of two evils - direct sun damage or the secondarydamage from free radicals triggered by a chemical blockers? At present, there is not enoughresearch data to provide a definitive answer. It appears at least some chemical sunblocksprevent more damage than they cause.

y Not all chemical sunblocks are created equal. For example, ecamsule (Mexoryl SX),homosalate and a few others appear to have a relatively good safety profile. On the otherhand, such agents as octocrylene, octinoxate, oxybenzone and sulisobenzoneappear to be

more damaging.If choosing a chemical sunscreen formula, examine the list of ingredientsand look up the information (on this site and elsewhere) on the specific blockers used in the

formula.

y Some manufacturers are attempting to mitigate the side effect of chemical sunscreens withnew technologies. One approach is microencapsulation: the sun blocking agent is encased intiny capsules, which makes it less prone to react with other chemicals and/or be absorbed bythe skin. Another approach is to add antioxidants to the sunscreen formula. Since much of thedamage from chemical sun blocks occurs due the increased production of free radicals, theaddition of an effective combination of antioxidants could be a mitigating factor. Yet anotherapproach is to add photostabilizers, which can modify the release of energy from chemicalsun blocks and thus reduce the consequent skin damage. If choosing a sunscreen withchemical blockers, opt for the ones employing at least some of these new technologies (ifavailable).

y Bottom liney

Evidence indicates that at least some absorbable chemical UV blocking agents (particularlyoctocrylene, octinoxate, oxybenzone and sulisobenzone) may cause damage to the skin uponexposure to sunlight. Until further research has established optimal usage practices, if any, for

these agents, it is prudent to put emphasis on other methods of UV protection, such asreducing sun exposure and using physical sunscreens. However, in some situations, thebenefits of chemical UV blockers may outweigh the risks. If so, one should try to usesunscreen formulas containing the least damaging of the chemical blockers and/or theformulas employing the methods to mitigating such damage, such as encapsulation,antioxidants and/or photostabilizers.

y Index ofwidely used UV-blockers by type and range

y


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y Physical: zinc oxide, titanium dioxide,

y Chemical: avobenzone (Parsol, Eusolex, Escalol), bemotrizinol (TinosorbS), benzophenone-3 (oxybenzone), benzophenone-4 (sulisobenzone), ecamsule(Mexoryl SX), phenylbenzimidazole sulfonic acid (ensulizole), homosalate, octylmethoxycinnamate (octinoxate), octyl salicylate (octisalate), octocrylene

y Hybrid: bisoctrizole (Tinosorb M)

y UVB blockers: phenylbenzimidazole sulfonic acid (ensulizole), homosalate, octyl

methoxycinnamate (octinoxate), octyl salicylate (octisalate), benzophenone-3(oxybenzone), benzophenone-4 (sulisobenzone)

y UVA blockers: avobenzone (Parsol, Eusolex, Escalol), ecamsule (Mexoryl SX),

y UVA+UVB blockers: zinc oxide, titanium dioxide, bisoctrizole (TinosorbM), bemotrizinol (Tinosorb S), octocrylene

Sunscreens and Photoprotection

Introduction

Encouraging photoprotection is the leading preventative health strategy used by physicians

involved in skin care. Although sun avoidance is most desirable, outdoor occupations andlifestyles make total avoidance impossible for many individuals. The regular use ofsunscreens represents a practical compromise in this regard. Sunscreens prevent the

formation of squamous cell carcinomas in animals. In humans, the regular use of sunscreenshas been shown to reduce actinic keratoses, solar elastosis, and squamous cell carcinoma.

1,2

Their effect on preventing melanoma is less clear. Drug photosensitization and photo-inducedor photo-aggravated dermatoses may be prevented with sunscreen use, especially with

products that offer better blockage in the UV-A range.

Additionally, the eMedicine Emergency Medicine article Sunburn and Pediatrics article

Sunburn may be of interest.

Definitions

UV radiation (UVR) that reaches the Earth's surface can be divided into UV-B (290-320 nm)

and UV-A (320-400 nm). UV-A can be further subdivided into UV-A I, or far UV-A (340-

400 nm), and UV-A II, or near UV-A (320-340 nm).

The US Food and Drug Administration (FDA) regulates sunscreen products as over-the-

counter drugs. The Final Over-the-Counter Drug Products Monograph on Sunscreens

(Federal Register 1999: 64: 27666-27963) established the conditions for safety, efficacy, and

labeling of these products. The sun protection factor (SPF) is defined as the dose of UVRrequired to produce 1 minimal erythema dose (MED) on protected skin after the application

of 2 mg/cm

2

of product divided by the UVR required to produce 1 MED on unprotected skin.A water-resistant product maintains the SPF level after 40 minutes of water immersion,

whereas a very water-resistant (formerly waterproof) product maintains the SPF level after 80minutes of water immersion. A broad-spectrum or full-spectrum sunscreen provides both

UV-B and UV-A protection, ideally through the entire UV-A I and UV-A II range.

A more recent proposed amendment (Federal Register 2007: 72: 49070) further elaborated onUV-B (SPF) and UV-A testing. To address the inadequacies of any single UV-A rating

system, the FDA proposes a combination spectophotometric (in vitro) and clinical (in vivo)


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UV-A testing procedure to allow for a non-numerical UV-A protection 4-star rating system,with 1 star being low protection and 4 stars being the highest.3

In Europe, sunscreen products are considered cosmetics, their function being to protect the

skin from sunburn. The Third Amendment of the European Economic Community Directive

provides a definition and lists the UV filters that cosmetic products may contain. The

European Union allows several ingredients not available in the United States.

Active Sunscreen Ingredients

Sunscreens have traditionally been divided into chemical absorbers and physical blockers on

the basis of their mechanism of action. Chemical sunscreens are generally aromaticcompounds conjugated with a carbonyl group. These chemicals absorb high-intensity UV

rays with excitation to a higher energy state. The energy lost results in conversion of theremaining energy into longer lower energy wavelengths with return to ground state. Physical

blockers reflect or scatter UVR. Recent research indicates that the newer microsized forms of

physical blockers may also function in part by absorption. Sometimes referred to as

nonchemical sunscreens, they may be more appropriately designated as inorganic particulatesunscreen ingredients. Allowable ingredients and maximum allowable concentrations, as

listed in the FDA monograph, are shown in the Table below. Sunscreen ingredients can also

be classified by the portion of UVR that they effectively absorb.

FDA Sunscreen Final Monograph Ingredients

Table

Drug Name Concentration, % Absorbance

Aminobenzoic acid Up to 15 UV-B

Avobenzone 2-3 UV-A I

Cinoxate Up to 3 UV-B

Dioxybenzone Up to 3 UV-B, UV-A II

Ecamsule* 2 UV-A II

Ensulizole Up to 4 UV-B

Homosalate Up to 15 UV-B

Meradimate Up to 5 UV-A II

Octocrylene Up to 10 UV-B

Octinoxate Up to 7.5 UV-B

Octisalate Up to 5 UV-B


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Oxybenzone Up to 6 UV-B, UV-A II

Padimate O Up to 8 UV-B

Sulisobenzone Up to 10 UV-B, UV-A II

Titanium dioxide 2 to 25 Physical

Trolamine salicylate Up to 12 UV-B

Zinc oxide 2 to 20 Physical

Drug Name Concentration, % Absorbance

Aminobenzoic acid Up to 15 UV-B

Avobenzone 2-3 UV-A I

Cinoxate Up to 3 UV-B

Dioxybenzone Up to 3 UV-B, UV-A II

Ecamsule* 2 UV-A II

Ensulizole Up to 4 UV-B

Homosalate Up to 15 UV-B

Meradimate Up to 5 UV-A II

Octocrylene Up to 10 UV-B

Octinoxate Up to 7.5 UV-B

Octisalate Up to 5 UV-B

Oxybenzone Up to 6 UV-B, UV-A II

Padimate O Up to 8 UV-B

Sulisobenzone Up to 10 UV-B, UV-A II

Titanium dioxide 2 to 25 Physical

Trolamine salicylate Up to 12 UV-B

Zinc oxide 2 to 20 Physical

*Only available in United States in patented products.


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Ultraviolet B

Padimate O

Para- aminobenzoic acid (PABA) was one of the first chemical sunscreens to be widely

available. Several problems limited its use. It required an alcoholic vehicle, it stained clothing,

and it was associated with a number of adverse reactions. Ester derivatives, mainly padimateO or octyl dimethyl PABA, became more popular, with greater compatibility in a variety of

cosmetic vehicles and a lower potential for staining and adverse reactions. Because ofproblems with PABA formulations, manufacturers emphasized the PABA-free claim, and

now both PABA and padimate O are less frequently used. Padimate O is the most potent UV-B absorber. The decline in its use, along with the demand for higher SPF products, has led to

the incorporation of multiple active ingredients into a single product to achieve the desiredSPF, replacing single PABA esters.

Octinoxate

The cinnamates have largely replaced PABA derivatives as the next most potent UV-Babsorbers. Octinoxate or Octyl methoxycinnamate is the most frequently used sunscreen

ingredient. Octinoxate is an order of magnitude less potent than padimate O.

Octisalate

Octisalate or octyl salicylate is used to augment the UV-B protection in a sunscreen.Salicylates are weak UV-B absorbers, and they are generally used in combination with other

UV filters. Other salicylates must be used in higher concentrations. They all have a goodsafety profile.

Octocrylene

Octocrylene may be used in combination with other UV absorbers to achieve higher SPF

formulas. Octocrylene used in combination with other sunscreen ingredients, such as

avobenzone, may add to the overall stability of these ingredients in a specific formula.

Ensulizole

Most chemical sunscreen ingredients are oils that are soluble in the oil phase of emulsion

systems, accounting, in part, for the heavy, greasy aesthetics of many of these products.

Ensulizole or phenylbenzimidazole sulfonic acid is water soluble, and it is used in products

formulated to feel lighter and less oily, such as daily use cosmetic moisturizers. It is a

selective UV-B filter, allowing almost all UV-A transmission.

Ultraviolet A

Oxybenzone

Although benzophenones are primarily UV-B absorbers, oxybenzone absorbs well through

UV-A II. Oxybenzone can be considered a broad-spectrum absorber. It significantly

augments UV-B protection when used in a given formula.


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Meradimate

Anthranilates are weak UV-B filters, and they absorb mainly in the near UV-A portion of thespectrum. Anthranilates are less effective in this range than benzophenones, and they are less

widely used.

Avobenzone

Often referred to by its trade name, Parsol 1789, butyl methoxydibenzoylmethane or

avobenzone provides superior protection through a large portion of the UV-A range,including UV-A I. It has been widely used in Europe for the last decade. The FDA recently

approved avobenzone for use in the United States. Potentially a significant addition tosunscreen products for true broad-spectrum UV protection, concerns have been raised

regarding its photostability and its potential to degrade other sunscreen ingredients inproducts in which it is used.

Ecamsule

Terephthalylidene dicamphor sulfonic acid or Mexoryl SX provides protection within the

near UV-A range (320- to 340-nm). It is only available in select patented sunscreen products

with the trade name Antihelios. Mexoryl SX is water soluble, making it less water resistant.

Also subject to photoinstability, it is combined with octocrylene to increase its photostability.

Physical blockers

Some of the original sunblocks were opaque formulations reflecting or scattering UVR.

During World War II, red petrolatum was extensively used by the military. Titanium dioxideand zinc oxide also functioned in this fashion. Poor cosmetic acceptance had limited the

widespread use of the latter 2 ingredients until microsized forms became available, also

known as inorganic particulate sunscreens.

Titanium dioxide

The ideal sunscreen agent would be chemically inert, safe, and absorb or reflect through the

full UV spectrum. Titanium dioxide meets these criteria limited only by aesthetics. By

decreasing the particle size of this pigment to microsize or ultrafine grades, thereby making itless visible on the skin surface, some of these advantages could be used. This ingredient can

be classified as a broad-spectrum agent.

Despite advances in the technology, formulating products with this ingredient that do notwhiten the skin secondary to pigment residue is difficult. Adding other pigments that simulate

flesh tones may partially camouflage this effect. The net effect may be that the user isinclined to use less of the product (a light application), effectively lowering the SPF. Hybrid

products that use a combination of chemical UV absorbers with inorganic particulate

sunscreens may represent a practical compromise.

Zinc oxide

Having been used for many years in opaque blocks, zinc oxide has recently been approved bythe FDA as an allowable active ingredient in sunscreen products. Like titanium dioxide,


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microsized or ultrafine grades of this ingredient have been developed, offering some of thesame advantages and disadvantages described above, including the ability to provide more

full-spectrum protection. Zinc oxide is less whitening in this form than titanium dioxide andprovides better UV-A I protection.

SPF Level

Arguably, a SPF 15 sunscreen provides full UV-B protection for healthy individuals. A SPF

15 product filters out more than 93% of UV-B radiation, and a SPF 30 product filters out less

than 97%. The difference of 4% would not seem significant to most individuals. Productapplication technique outside the laboratory alters the SPF. As previously noted, the standard

FDA method for SPF testing involves a sunscreen application thickness of 2 mg/cm2. Several

studies indicate that under in vivo, real-world conditions, application thickness more likely

approximates 0.5-1.0 mg/cm2, lowering the effective SPF of the product. When SPF testing is

conducted outdoors, the efficacy of products is found to be lower than in the laboratory.

Erythema, the key measurement in the SPF assay, is a relatively crude biologic endpoint. A

comparison of a SPF 15 sunscreen versus a SPF 30 sunscreen showed subclinical damage(sunburn cell formation) in the former without visible erythema. The SPF 30 productprovided significantly greater protection. Other forms of subclinical damage may occur with

a SPF 15 formulation. Although UV-A protection may be less than desirable with allsunscreen products, the UV-A protection is better with a higher SPF, particularly in the UV-

A II (320-340 nm) or shorter UV-A range.

UV-A Protection

Although sunscreens provide excellent UV-B protection, they lack in UV-A protection,

particularly UV-A I. With the availability of higher SPF products allowing individuals tospend greater amounts of time in the sun without burning, concerns have been raised about

the adequacy of the UV-A protection of these products. In fact, individuals relying onsunscreens as their sole form of photoprotection may now be subject to greater cumulative

sun exposure, including UV-A radiation.

No consensus exists about the best method for measuring UV-A protection. A variety of

methods have been proposed. The FDA proposal is referenced above (see Definitions).

Available methods have been reviewed in detail and summarized by Lowe. In vivo methods

have been developed on the basis of direct UV-A erythema, persistent pigment darkening,

and photosensitization with psoralens. A detailed discussion is beyond the scope of this

review. At best, each method has its limitations and indications for a particular clinicalsituation or skin type. An in vitro method relying on transmittance through a thin substrate,

such as thin film, may be more practical and is currently used in Europe. If protection from

UVR into the UV-A I range is desired, the formula should contain either avobenzone or an

inorganic particulate sunscreen as an active ingredient.

Sunscreen Vehicles

Vehicle type is critical for determining sunscreen efficacy and aesthetics. Ingredients, such as

solvents and emollients, can have a profound effect on the strength of UV absorbance by the

active ingredients and at which wavelengths they absorb. Film formers and emulsifiers


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determine the nature of the film that forms on the skin surface. Higher SPF products require aformula that provides a uniform and thick sunscreen film with minimum interaction of inert

ingredients with the actives. Durability and water resistance are obviously vehicle dependent.Lastly, product aesthetics play a large role in patient compliance with specific sunscreen

recommendations.

The most popular sunscreen vehicles are lotions and creams. Two-phase oil-in-water orwater-in-oil emulsion systems allow for the widest variety in formulation. Most sunscreen

ingredients are lipid soluble and are incorporated into the oil phase of the emulsion. Higher

SPF products may contain 20-40% sunscreen oils, accounting for the occlusive greasy feel of

many of these products. Dry lotions, often marketed as sport lotions, represent the

formulator's attempt to provide a less oily product. Newer "ultrasheer" products further refine

these qualities with the use of silica as a major vehicular component.

Other vehicles for organic sunscreen ingredients include gels, sticks, and aerosols. Water- or

alcohol-based gels provide less greasy aesthetics, but they rely on the more limited number of

water-soluble sunscreen ingredients and are less substantive with a greater potential for

irritation. Sticks readily incorporate lipid-soluble sunscreens thickened with waxes and

petrolatum and are heavier on application, but they are useful for protecting limited areas,such as the lips, the nose, or around the eyes. Aerosols provide some convenience on

application, but they may be difficult to apply evenly, resulting in a discontinuous film.

Sunscreens have been incorporated into a broad range of consumer products, including daily-

use cosmetics. The FDA monograph now distinguishes between beach and nonbeach

products. The availability of sunscreens in this fashion offers many advantages.

Daily protection is facilitated for a large segment of the population. UV protection is

encouraged by the glamour image associated with cosmetic use. Sunscreens/moisturizers are

available year-round, as opposed to seasonal beach products. Moisturizers that incorporate

sunscreens are generally oil-in-water emulsions. Water-soluble sunscreen ingredients areoften used to decrease the oil phase and to increase the cosmetic elegance. Foundation

makeup without sunscreen generally provides a SPF of 3 or 4 by its pigment content. Byraising the level of pigments, including inorganic sunscreen particulates, titanium dioxide and

zinc oxide, higher SPF can be achieved with or without the use of organic chemicalsunscreens. Makeup with sunscreen has intrinsic full-spectrum UV-A protection based on

opacity. Chemical sunscreens are generally added to lipsticks to provide enhanced SPFprotection.

Sunscreen agents have been combined with DEET (N, N,-diethyl-m-toluamide)containing

insect repellents, with a possible decrease in sunscreen efficacy and an increase in DEET

absorption. Combination products such as these should be used cautiously.

Photostability and Toxicity

Photostability refers to the ability of a molecule to remain intact with irradiation.

Photostability is potentially a problem with all UV filters because they are deliberately

selected as UVR-absorbing molecules. This issue has been raised specifically with

avobenzone, with photolysis demonstrated, especially in vitro systems, that simultaneously

irradiate and measure transmittance in situ. This effect may degrade other sunscreens in a


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formulation. This change has also been observed with octyl methoxycinnamate and octyldimethyl PABA, while oxybenzone was shown to be relatively stable.

Higher SPF sunscreen products have led to the use of multiple individual sunscreen agents

used in combinations at maximum concentrations that may interact. The photostability of the

molecules also depends on the solvent or the vehicle used. Certain ingredients may have a

stabilizing effect on others; octocrylene has been shown to photostabilize avobenzone. Therelevance of these observations to the in vivo situation remains unclear. Much work remains

to be completed in this area.

Subjective irritation associated with burning or stinging without objective erythema is the

most common sensitivity complaint from sunscreens. This irritation is most frequently

observed in the eye area. Persistent objective irritant contact dermatitis is more common than

and may be difficult to distinguish from true allergic contact dermatitis, although true allergy

to sunscreen ingredients is uncommon. Fragrances, preservatives, and other excipients

account for many of the allergic reactions that occur with sunscreens. Virtually all sunscreen

ingredients reported to cause contact allergy might be photoallergens. Although still

relatively uncommon, sunscreen actives seem to have become the leading cause of

photocontact allergic reactions. Individuals with preexisting eczematous conditions have asignificant predisposition to sensitization associated with their impaired cutaneous barrier.

Most individuals who develop photocontact dermatitis to sunscreens are patients withphotodermatitides.

Organic sunscreens, specifically PABA and its derivatives, have been the subject of extensive

in vitro photochemical and cytologic studies that suggest that organic sunscreens, such as

PABA, interact with DNA following UV radiation and might potentiate photocarcinogenesis.

Both acute and chronic in vivo animal studies show sunscreens to be protective for both UV-

induced DNA damage and skin tumor formation. Most significantly, routine sunscreen use in

humans has been shown to reduce solar elastosis, actinic keratoses, and squamous cell

carcinomas. The in vivo data would seem to eliminate concerns related tophotocarcinogenicity with the use of organic chemical sunscreens.

Sunscreens containing inorganic particulates (titanium dioxide and zinc oxide) provide a

good option for individuals with sensitive skin because these ingredients are not associatedwith irritation or sensitization. Absent demonstrable dermal penetration, concerns raised

about toxicity with the use of nanotechnology would seem unfounded with these ingredients.4

Vitamin D

Regular sunscreen use can diminish UV-dependent cutaneous synthesis of vitamin D. Elderly

persons are particularly susceptible to the consequences of vitamin D deficiency, including

osteopenia and bone fractures. Under conditions of actual usage, clinical trials have shownthat individuals instructed in carefully applying sunscreens still receive enough sunlight tomaintain normal vitamin D levels. Maximal vitamin D synthesis through UV exposure is

obtained with relatively low doses of erythemogenic UV achievable with sunscreen usage.Optimal vitamin D levels have not been defined. Ample vitamin D levels can be obtained

from incidental sun exposure, diet, and supplements. Some experts are recommending

supplements containing up to 1000 IU of vitamin D, particularly in older individuals.5


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Photoprotection

Sunscreens alone may provide insufficient protection from UVR. Sunscreens function best to

prevent sunburn from UV-B radiation. They provide more limited protection from UV-A

radiation. Sole dependence on sunscreens can have the unwanted effect of increasing outdoor

exposure times, particularly in those individuals who burn easily and tan poorly. Sun

avoidance remains the most desirable form of sun protection.

Simply staying indoors is obviously the best way of avoiding the sun. However, encouraging

individuals to time outdoor exposure to avoid the hours when the sun is at its zenith is morepractical. Trying to schedule activities before 10 am and after 4 pm (daylight savings time)

avoids solar exposure at times of peak intensity. Individuals need to be reminded that oncloudy days as much as 80% of UVR may still penetrate the cloud cover. Shade availability

in recreational areas is also desirable despite difficulty in accurately estimating the protectiveeffects with varying reflection and penetration in different environments. Window glass

absorbs most of the radiation below 320 nm; however, considerable amounts of UV-A

radiation may still pass through glass. Special plastic films containing UV-A shields as an

interleaf or overlay are available.

Clothing can be an excellent form of sun protection. The most important determinant is

tightness of the weave. Fabric type is less important. Thickness is also less important thanregular weave. Protection drops significantly when the fabric becomes wet. Color plays a

minor role, with dark colors protecting better than light colors. A crude test of clothing is tohold it up to visible light and observe the penetration. The FDA defines clothing with a SPF

rating as a medical device. One approved line of clothing with a rating of SPF 30 or greater isSolumbra (1-800-882-7860). Hats are the most important articles of clothing. A 4-inch wide

circumferential brim is required to cover the entire face and neck.

Sunscreen should be applied 15-30 minutes prior to sun exposure to allow sufficient time for

a protective film to develop. Sunscreen should be reapplied after prolonged swimming orvigorous activity. Under conditions of continuous UVR exposure, they should be reapplied

every couple of hours. Sunscreen needs to be applied liberally. As much as 1 oz may be

needed to cover the entire body. Particular attention needs to be paid to the back of the neck,

the ears, and the areas of the scalp with thin hair. Sunscreens represent only one component

of a total program of photoprotection.

PhysicalUVA+UVB sunscreen/sunblock:

Zinc Oxidey Generic name: Zinc oxide; Zn0

y Brand(s): Various

y Type: Physical

y Range ofUV spectrum covered: UVA (both UVA-1 and UVA-2), UVB

y Wavelengths covered: good uniform coverage between 290-400 nm, and some coverage upto 700 nm

y Stability:

Regular zinc oxide is highly stable under most conditions; minimal reactivity may occur,


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especially in direct sunlight. However, zinc oxide nanoparticles are far more reactive/catalyticthan regular zinc oxide powder and might promote the formation of harmful free radicals whenexposed to sunlight. Most manufacturers of zinc oxide nanoparticles coat them to reduce oreliminate such effects.

y Summary:Regular zinc oxide is one of the most broadly effective, established and safe sun blockingingredients available. Its major disadvantage is unsightly whitish tint it creates. Nanoparticle

forms are less unsightly but their potential risks are unclear and need to be more thoroughlyresearched. Also, it is difficult to achieve high SPF (UVB protection measure) with zinc oxidealone. Therefore, in high SPF sunscreens, it is generally combined with chemical UVBblockers.

Details:

PhysicalUVA+UVB sunscreen/sunblock:

Titanium Dioxide

y Generic name: Titanium dioxide; Titanium oxide; TiO2

y Brand(s): Various

y Type: Physicaly Range ofUV spectrum covered: UVA (better covers UVA-2 than UVA-1), UVB

y Wavelengths covered: good uniform coverage between 290-350 nm; insufficient coverage

between 350-400 nm, especially in microfine/nanoparticle forms

y Stability:Regular titanium dioxide is highly stable under most conditions. However, it has somephotocatalytic activity (i.e. promotes reactions between other chemicals), especially in directsunlight. Titanium dioxide nanoparticles appear to have much greater photocatalytic activitythan regular titanium dioxide powder and might trigger formation of harmful free radicals whenexposed to sunlight. Most manufacturers of titanium dioxide nanoparticles coat them toreduce or eliminate such effects.

y Summary:Titanium dioxide is a physical sunscreen protecting against UVB and short UVA (a.k.s. UNA-1)light. It has a long history of seemingly safe use and is not irritating. Its disadvantages include

unsightly whitish tint and insufficient protection against long UVA (a.k.a UVA-2). It may alsohelp generate harmful free radicals via photocatalytic mechanism when exposed to sunlight.These effects may not have significant impact in topical use but the issue needs to beresearched. Nanoparticle forms of titanium dioxide are less unsightly but their potential risksare unclear and may be greater than those associated with regular forms. More research isclearly needed. To increase protection and extend its range, titanium dioxide is usuallycombined with chemical UVB and UVA blockers and/or zinc oxide.

hemicalUVA sunscreen/sunblock agent:

Avobenzone

y Generic name: Avobenzone; butyl methoxydibenzoylmethane

y Brand(s): Parsol 1789, Eusolex 9020, Escalol 517 and others

y Type: Chemical

y Range ofUV spectrum covered: UVA (both UVA-1 and UVA-2)

y Wavelengths covered: 310-400 nm, which covers all of UVA

y Stability:Avobenzone degrades in the sunlight, which leads to loss of protective effect. The rate of

degradation can be reduced by photostabilizers. However, photostabilizers may increase therisk of skin irritation.


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y Summary:Abobenzone is one of the very few chemical sunscreens with good coverage of UVAspectrum. Abobenzone is relatively nonirritating, although, as with many skin care ingredients,the possibility of low-level topical or systemic toxicity with long-term use remainsunresearched. Abobenzone degrades in sunlight (especially if mixed with inorganicsunscreens) and loses effectiveness over time. Development of stabilized andmicroencapsulated versions of avobenzone is promising and may reduce the above

drawbacks.

hemicalUVA+UVB sunscreen/sunblock:

Bemotrizinol (Tinosorb S)

y Generic name: Bemotrizinol; bis-ethylhexyloxyphenol methoxyphenyl triazine

y Brand(s): Tinosorb S

y Type: Chemical

y Range ofUV spectrum covered: UVA (both UVA-1 and UVA-2), UVB

y Wavelengths covered: about 280-400 nm, which covers both UVB and UVA ranges; peakprotection at 348 nm

y Stability:Bemotrizinol is stable when exposed to sunlight. It can also partly protect other chemicalsunscreens (e.g. UVA-blocker avobenzone) from degradation.

y Summary:Bemotrizinol is one of the very few chemical sunscreens with good coverage of the entireUVA spectrum. It also provides some UVB protection. Furthermore, it does not degrade undersunlight and is not significantly absorbed into the skin. Overall, it appears to have a goodsafety profile, even though current safety data are insufficient and long-term human safetystudies are lacking.

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Sun Protection Basics